What is lung cancer? Lung cancer is a common cancer of the respiratory system that occurs when there is an uncontrolled growth of abnormal cells in the air passages of the lung. Lung cancer is the deadliest cancer in both men and women, according to the National Institutes of Health. The main cause of lung cancer is smoking. While not usually noticed until later in the disease, lung cancer symptoms include fatigue, chest pain, difficulty breathing, and worsening and persistent cough, which may bring up bloody sputum. Lung cancer treatment advances have improved the prognosis and survival rates for many people with this type of cancer. Women who have never smoked may be more at risk for lung cancer than men who have never smoked. In fact, 47% of cases of lung cancer occur in women, and one in five women with lung cancer has never smoked. In contrast, only one in 10 men with lung cancer has never smoked, according to the National Lung Cancer Partnership. As cancer progresses and metastasizes, it interferes with vital processes and functions of the lungs and other organs where it has spread. Seeking regular medical care offers the best chances of discovering lung cancer in its earliest, most curable stage. If you have lung cancer, following your treatment plan may help reduce your risk of some complications of lung cancer. Lung cancer is a highly preventable cancer because the majority of cases are caused by smoking. Quitting smoking greatly reduces your risk of lung cancer. Diagnosing lung cancer in its earliest stage provides the best hope for successful treatment and a cure. If you currently smoke or have a history of smoking, talk with your doctor about testing for lung cancer.